The invention relates to high-definition sonars used for submarine imaging. It concerns in particular sonar means enabling identification of objects buried in sedimentary layers. It also concerns detection systems using such a sonar mounted on a self-propelled submarine vehicle.
In this field there are known techniques consisting in towing a “sonar towfish” equipped with sonar means operating in parametric mode, in other words transmitting at two high frequencies, typically about one hundred kHz, and receiving at the lower beat frequency. This technique is described for example in the French patent no. 2 509 869 filed on 17 Jul. 1981 by the company SINTRA-ALCATEL under the number 81 213 961.
This technique has a major disadvantage associated with the parametric mode, which is a transmission loss of about 30 to 40 dB.
In the U.S. Pat. No. 6,160,756 filed on 15 Jun. 1998 by GUIGNE International Ltd and published on 12 Dec. 2000, a system for seafloor imaging is described employing a sonar also operating in parametric mode and designed to move slowly near the seabed ensonifying it vertically. The antenna is notably mounted on a tracked vehicle that moves across the seabed. This technique has the disadvantages of having a small intercept and requiring a large number of transducers, the antenna being flat-mounted (2 dimensional).